Chitosan, a polycationic biopolymer of (1-4)-linked 2-amino-2deoxy-D-glucopyranose, is an abundant natural polysaccharide, which is well known for the superb capacity to adsorb contaminants and heavy metals and kill the bacteria in gases and water. Thus it is a good candidate for fabricating a filtering medium to disinfect and purify the gases and water. However, most conventional filters are not self-regenerative and require replacement regularly after the filter is fully accumulated with contaminants. The pore size of conventional filter medium is also not readily manipulated to suit various particulates. Other problems such as fixed surface charge and low mechanical strength also need to be addressed in the present invention.